The Power of Babel: A Natural History of Language John McWhorter 327pp, Heinemann, £16.99

The story of Babel, as told in Genesis, is one of presumption and punishment, echoing the story of the Fall itself. Once, "the whole earth was of one language". Its monoglot speakers projected "a tower, whose top may reach unto heaven"; God, seeing that "nothing will be restrained from them", shattered that language into a multitude of mutually incomprehensible ways of speech. The builders left off their proud construction; "Therefore is the name of it called Babel."

The myth of Babel (from the Hebrew verb meaning "to confuse") tells of a loss of wholeness, as if the diversity of human languages were proof of the endless dividedness of peoples from one another. For John McWhorter, Babel is more like the name of a life force. He simply loves the variety and flux of particular languages, and his book is an example-rich, sometimes anecdotal tribute.

The breathless tour of linguistic oddities from around the globe has its own empirical delight. Where Steven Pinker's bestselling The Language Instinct was somewhat austerely dedicated to language in its most general aspects, The Power of Babel is about languages in the plural: their eccentricities and "baroque" complexities. The illustrations are chosen to denaturalise one's assumptions about language. We find the languages of "primitive" peoples with ineffably complex grammatical rules, and are shown languages happily doing without any of the features that we might think vital to communication. There are languages of New Guinea that have no tenses; Australian languages with only three verbs.

McWhorter is a kind of linguistic David Attenborough, observing with an awed enthusiasm all the strange varieties and ingenious adaptations of the 6,000 or so human languages supposedly being spoken on the planet at this moment. The fascination is in his detail, the sheer case-by-case weirdness of languages. Here you can find out why the nouns in all those other European languages divide up into genders, and see how the strangeness of German ("die Gabel", "der Löffel" and "das Messer" for "fork", "spoon" and "knife") pales alongside the 16 genders of the Fula language of west Africa. Anyone who has sweated over Latin or Ancient Greek in school will have had a much easier time than if certain North American indigenous languages, with their dizzying inflections, had been set for GCSEs.

Everywhere language grows into curlicues of complication. There are the impossibly unpredictable plurals of the Luo language of Kenya, and the pedantic "evidential markers" of Tuyuca spoken in the Amazon rainforest (a statement has to be accompanied by a grammatical indication as to how one came by the information). Where there are not inflections, there are almost unlearnable sound-markers of grammatical function: the clicks of Southern African languages or the six-toned sound varieties of Cantonese.

For McWhorter, this variety is God's plenty. He particularly relishes the phenomenon that most nettles linguistic opinionists: language change. We usually see only the smallest hints of great, slow changes that are happening all the time. We hear the rise of slang, and sometimes its transformation into a standard part of the language. Occasionally we detect some grammatical element that is dying (to groans from the punctilious) or being born. Yet these are tiny things when measured against the continental shifts in language that happen over stretches longer than any single lifetime.

Palaeontologists have fossils; linguists have creoles. Unlike life-forms, new languages are, now and then, "created". First of all, "pidgin" versions of languages are developed when new speakers need to reduce a language to its most basic elements. A creole is what happens when a pidgin starts coming to life, developing its own inflections. Linguists can study the process, the unfolding of which is one of McWhorter's most intriguing subjects. He takes the case of "Tok Pisin" of Papua New Guinea: English "crushed to powder" and reborn according to Melanesian grammatical habits.

Knowing that self-transformation is a "natural" condition for speech, professors of linguistics always find it easy to condescend to those who fret about language change. The activities of the Association for the Preservation of the German language, which campaigns against the use of "downsize" instead of "abbauen" or "highlight" instead of "Höhepunkt", may indeed be "utterly futile" when seen in the long perspective of a language's irresistible self-transformation. The vigilance of the Académie Française against encroaching English words does seem to stem from the misconception that a language is its vocabulary - rather than its grammar, its patterns of sound, its rhythms of expression.

"Sounds are too volatile and subtle for legal restraints," observed Samuel Johnson in the preface to his great Dictionary. "To enchain syllables, and to lash the wind, are equally the undertakings of pride." Yet McWhorter himself is not always sure what he thinks of all this change. He talks frequently of the "evolution" of languages, but sometimes seems uncertain about this metaphor. On the one hand, all the incredibly various languages of the world are taken to have evolved from a single progenitor. There was, probably 150,000 years ago, an Ur-language, some of whose characteristics linguists can guess at. Out of it grew everything. On the other hand, languages do not necessarily change from the simple to the more complex. Is French a more "developed" language than the Latin from which it grew?

McWhorter reveals himself through his own ways with language, which one could call "Californian": fearing teacherliness, he uses homely reminiscences and irreverent analogies. This might seem like proselytising enthusiasm, but it is something more. Language, for him, lives in speech - that brief "mouthful of air", as Anthony Burgess called it. He is altogether less keen on the language as it is written, with its stern conventions and its distance from mere utterance. So when he quotes approvingly, it is invariably from TV or popular song. Author he may be, but he wants to be chatting rather than writing.

Writing, and particularly printing, are what change the evolutionary patterns that McWhorter finds himself calling "natural" to language. Literacy involves standardisation and the written language resists change, where speech rushes to meet it. English changes more slowly than it used to. We can understand the language of Shakespeare, who wrote some 400 years ago, but he would have found the Old English of 400 years earlier a foreign language. With widespread literacy come prescriptions that radically slow change.

Everything to do with correctness irks McWhorter, as it irked Pinker. Linguists know, of course, that common "errors" or infelicities are invariably uses of language that simply obey different codes from the "standard". A double negative ("I ain't doing nothing") is no less rational than a single one ("I'm not doing anything"). Yet, as they unravel the strange structures of languages, we should notice what linguists cannot tell us about. They have nothing to say about eloquence, wit, beauty, expressiveness, or any number of the special qualities of speech and writing.

Near the end of his book, McWhorter permits himself a grumble against the predominance in academic life of Chomskyan linguists (Pinker is one) dedicated to "illuminating the possibility that we possess a neural mechanism calibrated to produce basic sentences". More of them should be out in the field instead, charting one of the world's actual, dying languages. He points out that 96% of the world's population speak one of the "top 20" languages; many of the other indigenous languages will soon be no more. McWhorter will, he tells us, document one of them as soon as his book is finished; whether with sadness or with delight, it is hard to say.

· John Mullan is senior lecturer in English at University College, London. He is writing a book about anonymity for Faber.